This invention relates to a field emission cold cathode and, in particular, to a method of manufacturing the same.
A field emission cold cathode is known as an electron source of an electron gun for use in a cathode ray tube (CRT) or a flat display panel of a self-emission type.
Such a field emission cold cathode comprises a cathode chip or an emitter chip known in the art. After the cathode chip is formed, the field emission cold cathode is exposed to the atmosphere during transfer to a subsequent step or during execution of the subsequent step. Therefore, it is assumed that an oxygen or a carbon-based gas contained in the atmosphere is adsorbed onto the cathode chip through a surface thereof. This results in producing an unfavourable layer along the surface of the cathode chip.
Generally, field emission known in the art has an electron emission characteristic greatly dependent upon the work function of the surface of the cathode chip. When adsorbed onto the surface, the oxygen or the carbon-based gas fluctuates the work function. Under the circumstances, the field emission cold cathode suffers decrease of emission current and increase of current fluctuation, if it is exposed in the atmosphere. Therefore, it is required to clean the surface of the cathode chip.
In order to clean the surface of the high-melting-point metal material, use can be made of a relatively simple method in which high-temperature heat treatment is carried out in a high vacuum at a heat treatment temperature not lower than 1500.degree. C. However, the relatively simple method can not be applied to manufacture of the field emission cold cathode. This is because the heat treatment temperature has an upper limit strictly restricted on the reason which will later be described in conjunction with the drawings. Accordingly, it is disadvantageous that the surface of the cathode chip can not be completely cleaned.